1. Field of the Invention
This invention relates to a process for producing an azide-substituted aromatic polymer and to the novel azide-substituted aromatic polymers (e.g. polysulfones) so produced.
Azides are known to be thermally and photochemically labile groups capable of being readily transformed into a number of other useful derivatives, for example, primary amines which are themselves difficult to directly attach to polymers.
2. Description of the Prior Art
Several examples of polymeric alkyl azides produced by chemical modification of polymers have been reported in the literature. Typically, azide groups are introduced onto polymers containing chloroalkyl groups by reaction with sodium azide. The azides can then be converted to various other derivatives. Specifically, Cohen has reported the preparation of several 1,3-dipolar cycloaddition products from poly(vinylbenzyl azide.
However, as will be apparent hereinafter, the azidization of aromatic polymers cannot be done in this manner, and insofar as Applicants' are aware, azide derivatives of aromatic polymers, including polyphenylene ethers, polysulfones, halogenated polysulfones, polyarylsulfones, halogenated polyarylsulfones, polyvinylthiophenes, polystyrenes, halogenated polystyrenes and co-polymers thereof have not been made heretofore.
Polysulfone is an engineering thermoplastic widely used as a membrane material in the area of liquid and gas separations. It has been a goal of Applicants' work to tailor the membrane separation characteristics of this polymer and increase the scope of its use by introducing various functional groups by chemical modification. For example, we have obtained several U.S. Patents on the subject of direct lithiation and halogenation-lithiation of polysulfones as a means of producing carboxyl, hydroxyl and a number of other derivatives. See the following U.S. Patents.
Direct lithiation of polysulfone.
U.S. Pat. No. 4,797,457, issued Jan. 10, 1989, Preparation of substituted polysulfones through ortho-metalated intermediates, M. D. Guiver, J. W. ApSimon & O. Kutowy. U.S. Pat. No. 4,833,219, issued 23 May 1989, Preparation of substituted polysulfones by metalation, M. D. Guiver, J. W. ApSimon & O. Kutowy.
Halogenation of polysulfone
U.S. Pat. No. 4,996,271, issued 26 Feb. 1991, A Method of Manufacturing Halogenated Aromatic Polysulfone Compounds and the Compounds so Produced, M.D. Guiver & O. Kutowy.
Halogenation-lithiation of polysulfone
U.S. Pat. No. 4,999,415, issued 12 March 1991, Aromatic Polysulfone Compounds and their Manufacture, M.D. Guiver & O. Kutowy.
Lithiated polymers can be converted to aminated polymers by reacting the lithiated polymer with a primary amine electrophile. Typically, this electrophile is methoxylamine or the lithium salt of methoxylamine. While this reagent works well with many smaller lithiated molecules, it is generally not an efficient reagent when used for polymer amination.
As an example from our experiments, when the lithium salt of methoxylamine (i.e. CH.sub.3 ONHLi) was reacted with a lithiated polysulfone containing an average of 1.2 lithium atoms per repeat unit, only 17% conversion of Li atoms to amine groups (DS=0.20) occurred and the polymer underwent some crosslinking.
Hinke and Staude, J. Appl. Polym. Sci., 42, 2951-2958 (1991), report that the amination of lithiated polysulfone with methoxylamine (not the lithium-salt i.e. CH.sub.3 ONH.sub.2) gave aminated polysulfone of DS only 0.12.
Other primary amine electrophile reagents which are reported to convert lithium atoms to amine groups in small molecules are ineffective when applied to lithiated polysulfone.
Trimethylsilyl azide reacts with a lithiated polysulfone to give a trimethylsilyl group rather than an azide which can be readily converted to a primary amine. Trimethylsilylmethyl azide does not react at all, and diphenylphosphoryl azide reacts to give a product that is not an azide or an amine.
It was also a goal of our work was to develop a better method than the conventional nitration-reduction pathway for derivatization of aromatic polymers such as polysulfones, with primary amine groups. While nitration of smaller molecules is a very common and useful procedure, a frequent problem with nitration of polymers is the tendency for chain degradation to occur. The resulting nitrated polymers are relatively resistant to reduction and can lead to incompletely reduced products. As well, we have experienced difficulty in our laboratory isolating the reduced polymers by some of the reported literature procedures.
It is known to use tosyl azide to convert small lithiated molecules to azides and primary amines (see J. Reed and V. Sniekus, below), but the approach has not been applied to any polymer systems to the best of our knowledge. As mentioned before, there are many reagents available for this type of conversion. Many of these are ineffective in that they cause chain degradation, chain crosslinking, have poor conversion efficiency or they do not work at all when applied to polymer modification.
The following are references on the use of tosyl azide in the conversion to azides:
Use of tosyl azide for converting non-polymeric lithiated molecules into amino derivatives:
General Route for the Facile Transformation of Ortho-Substituted Lithiobithienyls into Amino Derivatives, P. Spagnolo and P. Zanirato, J. Org. Chem., 47, 3177-3180 (1982).
Ortho-Amination of Lithiated Tertiary Benzamides. Short Route to Polysubstituted Anthranilamides, J. N. Reed and V. Sniekus, Tetrahedron Lett., 24, 3795-3798, (1983).
A review of amination reagents can be found in the reference: Electrophilic Amination of Carbanions, E. Erdik and M. Ay, Chem. Rev. , 89, 1947-1980 (1989).
Modification of other polymers to polymeric azides, namely, poly (vinylbenzyl chloride) to poly (vinylbenzyl azide), has been reported by H. L. Cohen, J. Polym. Sci., Polym. Chem., 19, 1337-1347 (1981). Conversion of poly-haloethyl acrylates, poly(vinyl chloride), poly(epichlorohydrin) and other poly(halohydrins) to polymeric azides has been reported by H. L. Cohen, Preparation of Polymeric Azides. II. The Preparation and Reactions of Various Polymeric Azides. J. Polym. Sci., Polym. Chem., 19, 3269-3284 (1981). In the latter paper, references are also made to the work of other authors for converting poly(vinyl chloride), poly (epichlorohydrin) and poly (3-chloromethyl-2,6-dimethylphenylene oxide) to polymeric azides.
To obtain the azide, the above prior art uses an approach in which, in most cases, an aliphatic chloride functional group on the polymer is converted with sodium azide. This requires the presence of an aliphatic chloride group (i.e. chloromethyl or chloromethylene) to work.